The present invention relates to a CPU (Central Processing Unit) core voltage switching circuit for reducing the power consumption of a CPU.
Conventionally, a CPU core voltage switching circuit, to which the present invention pertains, has been used primarily in reducing the power consumption of the CPU. With respect to such a CPU core voltage switching circuit, used recently in personal digital assistants (PDA), there is need to reduce power consumption in a terminal.
Conventionally, the CPU core voltage switching circuit used in a personal digital terminal (or assistant) requires a constant CPU core voltage.
However, there are problems encountered in the course of investigations toward the present invention. That is, the problems with the prior art reside in that, because the CPU core voltage (or the switching circuit thereof) requires a constant voltage, it is impossible to reduce power even when a slow CPU CLK (CPU clock pulse) is used or the load is reduced.
In view of the foregoing, it is an object of according to an aspect of the present invention to provide a low power-consumption CPU core voltage switching circuit.
It is another object according to another aspect of the present invention to provide a novel improved personal digital terminal or assistant. According to the present invention the CPU core voltage switching circuit is configured as described below.
According to a first aspect of the present invention, there is provided a CPU core voltage switching circuit installed in a personal digital assistant wherein, when the personal digital assistant is using (or performing) an application software product, CPU clock frequency is reduced to a half of a frequency used when the personal digital assistant is in an initial start state or a memory data initialization state.
According to a second aspect of the present invention, there is provided a CPU core voltage switching circuit wherein the CPU clock frequency used when the personal digital assistant is using an application software product is reduced to the half of a frequency used when the personal digital assistant is in the initial start state or in the memory data initialization state to make a CPU core voltage used when the personal digital assistant is using the application software product lower than a voltage used when the personal digital assistant is in the initial start state or in the memory data initialization state.
According to a third respect of the present invention, there is provided a CPU core voltage switching circuit wherein the CPU clock frequency is 33 MHz when the personal digital assistant is in the initial start state or in the memory data initialization state, and wherein the CPU clock frequency is 16.5 MHz when the personal digital assistant is using the application software product.
According to a fourth aspect of the present invention, there is provided a CPU core voltage switching circuit wherein the CPU clock frequency is set to 33 MHz to set the CPU core voltage to a first voltage (e.g., 2.7 V) when the personal digital assistant is in the initial start state or in the memory data initialization state, and wherein the CPU clock frequency is set to 16.5 MHz to set the CPU core voltage to a second voltage (e.g., 2.0 V) which is lower than the first voltage when the personal digital assistant is using the application software product.
According to a fifth aspect of the present invention, there is provided a CPU core voltage switching circuit, comprising a gate module outputting an input voltage as a CPU core voltage in response to a voltage control signal representing a high voltage; a voltage decreasing module decreasing an input voltage in response to a voltage control signal representing a low voltage and outputting the input voltage as the CPU core voltage; and a voltage switching control module increasing the CPU clock frequency and outputting a voltage control signal representing the high voltage to the gate module if the control signal indicates that the personal digital assistant is in the initial start state or in the memory data initialization state and for decreasing the CPU clock frequency and outputting a voltage control signal representing the low voltage to the voltage decreasing module if the control signal indicates that the personal digital assistant is using the application software product, the voltage control signal being responsive to the control signal input to the personal digital assistant from an external unit.
According to a sixth aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a gate module is a field effect transistor which receives an input voltage at a source terminal (S), receives a voltage control signal representing a high voltage at a gate terminal (G), and outputs the CPU core voltage at a drain terminal (D).
According to a seventh aspect of the present invention, there is provided a CPU core voltage switching circuit as defined by claim 5 wherein the voltage decreasing means is a regulator which receives the input voltage at an input terminal, receives the voltage control signal representing the low voltage at a control terminal, and outputs an output terminal voltage as the CPU core voltage at a drain terminal.
According to an eighth aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a voltage switching control module comprises a hybrid IC (Integrated Circuit) which increases the CPU clock frequency if the control signal indicates that the personal digital assistant is in the initial start state or in the memory data initialization state and decreases the CPU clock frequency if the control signal indicates that the personal digital assistant is using the application software product; and an RS flip-flop and an OR circuit which, in response to the CPU clock frequency, output a voltage control signal representing a high voltage to a gate module if the CPU clock frequency is high, and outputs a voltage control signal representing a low voltage to the gate module if the CPU clock frequency is low.
According to a ninth aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a hybrid IC comprises a CPU and a system controller.
According to a tenth aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a hybrid IC sets the CPU clock frequency to a high frequency (e.g., 33 MHz) if the control signal indicates that the personal digital assistant is in the initial start state or in the memory data initialization state and sets the CPU clock frequency to a half of said high frequency (e.g., 16.5 MHz) if the control signal indicates that the personal digital assistant is using the application software product.
According to an eleventh aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a gate module outputs a high input voltage as a CPU core voltage (e.g., of 2.7 V) in response to the voltage control signal representing the high voltage.
According to a twelfth aspect of the present invention, there is provided a CPU core voltage switching circuit, wherein a voltage decreasing module decreases the input voltage in response to the voltage control signal representing a low voltage and outputs low input voltage as the CPU core voltage (e.g. of 2.0 V).
According to a thirteenth aspect of the present invention, there is provided a personal digital assistant comprising the CPU core voltage switching circuit according to the first aspect.
According to a fourteenth aspect of the present invention, there is provided a personal digital assistant comprising the CPU core voltage switching circuit according to the fifth aspect, or any of other aspects relating to the voltage switching circuit.